Various configurations of waveguide systems have been used to combine multiple radio frequency (RF) signals into sum and difference combinations. One common application for such a waveguide configuration is a mono-pulse antenna system. In a mono-pulse antenna system, an RF signal is received at an antenna with two or more regions disposed about a bore sight. One or more angles from the bore sight of the incoming RF signal—and thus the target from which the mono-pulse RF signal came—can be determined from sum and difference combinations of RF signals from the two or more antenna regions. Aspects of the present invention include an improved waveguide comparator subsystem that can combine RF signals to produce sum and difference combinations. Embodiments of the invention can have particular application in mono-pulse antenna systems, which can be part of a mono-pulse tracking system or a mono-pulse data link system, and in other applications in which sum and difference combinations of two or more RF signals (e.g., mono-pulse radar systems) are determined.